Improved Directional Hydrogen Bonding Interactions for the Prediction of Activity Coefficients with COSMO-SAC

In a recent work, Chen and Lin showed that the consideration of directional hydrogen bonding in the COSMO-SAC model significantly improves the description of solvation properties of the associating fluids. In their method, the direction of a hydrogen bond was determined based on VSEPR theory; however, this geometric approach does not reflect the local electronic environment of the lone pairs and cannot be applied to certain molecules such as DMSO and HF. In this work, we adopt a new scheme that determines the hydrogen bond acceptors of a molecule based on the minima in the molecular electrostatic potential (MESP). The hydrogen bonding directions thus determined result in improvements (about 5-7% for VLE) in the prediction of the COSMO-SAC model for a variety of thermodynamic properties and phase equilibria, such as vapor-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE), the infinite dilution activity coefficient (IDAC), and the octanol-water partition coefficient (K-ow) calculations.